PHEVs have additional packaging challenges due to the much bigger battery and the inclusion of conventional gasoline components such as a fuel tank. Therefore, it is very likely that these difficulties are related to the hybrid version of the Niro, and less likely to be specific to the electric-only variant.
Interestingly, the Sportage PHEV lacks a spare tire, although the Sorento PHEV is equipped with one.
It may be worth considering a hitch with a spare tire attachment for the Niro PHEV, however its feasibility is uncertain.